1. Field of the Invention
The invention concerns a thick matter pump, with two delivery cylinders communicating with a material feed basin via openings situated on an end face, with two hydraulic drive cylinders connected to a reversible hydraulic pump via connections at the piston rod side or piston head side, with a swing oil line connecting the drive cylinder ends opposite to the pump with each other, the drive pistons of the drive cylinders and the delivery pistons of the delivery cylinders being pair-wise rigidly connected with each other via common piston rods, with equalizing lines connected in the area of the two ends of the drive cylinders bridging over the drive pistons at their respective end positions and containing a check or back pressure valve, and with two position sensors provided a defined distance from one of the ends of the drive cylinders, connected to a control device and emitting an end position signal as the associated piston passes by, for controlling the reversal of the hydraulic pump.
2. Description of the Related Art
Two-cylinder thick material pumps of this type are known, in which the two position sensors are provided on one of the two drive cylinders (EP-B 0 446 206). On the other drive cylinder no monitoring of the end position is carried out. It has been found that, depending upon the pressure relationships existing within the cylinder, leakages bypassing the piston can occur, which result in an accumulation of swing oil or in a loss of swing oil, which in turn can result in an advancing or retarding of one of the pistons.
Thus, for example in the case that low oil pressure oil is being supplied to the piston rod side, as for example during the cleaning operation with water, there may result an accumulation of swing oil. This leads thereto, that the piston in the second cylinder is caused to advance, as a result of which this piston when in the end position can come into an undesired slamming mechanical contact with the cylinder. On the other hand, in the case of a high-pressure operation, that is, in the process of thick material conveyance, there can result a loss of swing oil loss as a consequence of a leakage oil bypassing the piston. Thereby in the second cylinder the piston stroke is shortened, so that in the delivery cylinder a clot or plug—hardened concrete—can form. This concrete clot is not pushed out of the delivery cylinder but rather is sucked back in during each suction stroke of the delivery cylinder. It eventually hardens and leads to an elevated friction wear in the delivery cylinder.
In the case of the piston head side connection of the drive cylinder to the hydraulic pump, there results in the low-pressure operation a loss of swing oil. This results in advancing of one of the pistons and in the undesired end-position slamming of the piston in the second cylinder. In high-pressure operation there results in this situation an accumulation of swing oil, which due to the premature switching-over in the first cylinder, can lead to development of a plug in the second cylinder with the above described disadvantages.